The present invention relates to methods of producing agglomerated materials such as pellets or briquettes well suited for use as blast furnace charge and feed for iron making, and more particularly the invention relates to a method of producing agglomerates so designed that very fine materials having a wide distribution of particle sizes, e.g., fine iron ores unsuited for use with the conventional agglomerating processes such as sintering and pelletizing are formed, along with solid fuel, into pellets, briquettes or the like and the formed material is fired in a travelling grate-type furnace.
The present invention is intended to produce agglomerates having excellent economy and having excellent high-temperature properties as blast furnace charge and feed over those of the conventional processes from raw materials such as fine iron ores of the particle sizes which have been unsuited for use as raw materials.
It is well known in the art that generally there is a proper range of particle sizes for the fine ores used as raw materials in the production of sinters and pellets. With the DL-type sintering process, for example, the raw material is usually charged onto a grate without any formation. As a result, there is a requirement that the raw material fine ore should preferably include less than 10% (by weight) of the ore having the particle size of less than 125.mu. from the standpoint of ensuring the desired permeability. Also, since the product is subjected to crushing and sizing, the product yield is deteriorated and amounts to about 70%. In the case of the travelling grate-type pelletizing process, the fine iron ore must be formed into pellets by a preliminary processing operation. As a result, the particle size distribution of the raw material fine ore must be such that the ore contains 60 to 90% (by weight) of the material of less than 44.mu. so as to be formed into pellets smoothly. Also, the pellets are indurated by a burner above the grate using the down draft and the upper and lower layers of the pellets on the grate differ in heat pattern from each other thus causing variations in the product quality.
The agglomerate manufacturing method proposed in Japanese Laid-Open Patent Publication No. 55-107741 is similar in operation to the present invention in that it involves a preliminary heating operation prior to the ignition and it is still different from the subject matter of the invention in the following points thus making it impossible to obtain the effects of the present invention:
(i) The material is not a formed material (pellets or briquettes). PA0 (ii) A high-coke layer having a coke content of over 30% (by weight) is formed in thickness ranging from 3 to 4 mm. PA0 (iii) The preliminary heating operation involves only the downward gas flow.
Also, a preliminary treating method for fine sintering material is proposed in Japanese Patent Publication No. 56-2134 in which a portion of carbonaceous matter is added to the sintering material containing 15 to 35% (by weight) of fine iron ore of less than 125.mu. and the material is then subjected to a primary pellet forming operation. Then, the surface of the primary pellets are coated with the carbonaceous matter and converted to secondary pellets. The preliminary treating method then mixes the secondary pellets with 6 to 15% (by weight) of additional minipellets of which over 75% (by weight) has the particle size of 1 to 7 mm. As a result, this proposed process differs from the construction of the raw formed material according to the invention and hence the subject matter of the invention in that the surface of the pellets are coated only with the carbonaceous matter and that the coated pellets are further mixed with the minipellets.